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A DNS-based Blackhole List (DNSBL) or Real-time Blackhole List (RBL) is an effort to stop email spamming. It is a "blacklist" of locations on the Internet reputed to send email spam. The locations consist of IP addresses which are most often used to publish the addresses of computers or networks linked to spamming; most mail server software can be configured to reject or flag messages which have been sent from a site listed on one or more such lists. The term "Blackhole List" is sometimes interchanged with the term "blacklist" and "blocklist". A DNSBL is a software mechanism, rather than a specific list or policy. There are dozens of DNSBLs in existence,〔(【引用サイトリンク】 title=DNS & RHS blackhole lists )〕 which use a wide array of criteria for listing and delisting of addresses. These may include listing the addresses of zombie computers or other machines being used to send spam, ISPs who willingly host spammers, or those which have sent spam to a honeypot system. Since the creation of the first DNSBL in 1997, the operation and policies of these lists have been frequently controversial,〔(【引用サイトリンク】 title=RFC6471 )〕〔(【引用サイトリンク】 title=RBLMon.com: What are RBLs and How do they Work? )〕 both in Internet advocacy and occasionally in lawsuits. Many email systems operators and users〔(【引用サイトリンク】 title=Revealing Botnet Membership Using DNSBL Counter-Intelligence )〕 consider DNSBLs a valuable tool to share information about sources of spam, but others including some prominent Internet activists have objected to them as a form of censorship.〔(【引用サイトリンク】 title=RBL Criticism )〕〔(【引用サイトリンク】 title=Electronic Frontier Foundation, EFFector, Vol. 14, No. 31, Oct. 16, 2001 )〕〔(【引用サイトリンク】 title=Verio gags EFF founder over spam )〕〔(【引用サイトリンク】 title=Choosing Spam over Censorship )〕 In addition, a small number of DNSBL operators have been the target of lawsuits filed by spammers seeking to have the lists shut down.〔(【引用サイトリンク】 title=EMarketersAmerica.org sues anti-spam groups )〕 == History of DNSBLs == The first DNSBL was the Real-time Blackhole List (RBL), created in 1997, at first as a BGP feed by Paul Vixie, and then as a DNSBL by Eric Ziegast as part of Vixie's Mail Abuse Prevention System (MAPS); Dave Rand at Abovenet was its first subscriber. The very first version of the RBL was not published as a DNSBL, but rather a list of networks transmitted via BGP to routers owned by subscribers so that network operators could drop all TCP/IP traffic for machines used to send spam or host spam supporting services, such as a website. The inventor of the technique later commonly called a DNSBL was Eric Ziegast while employed at Vixie Enterprises. The term "blackhole" refers to a networking black hole, an expression for a link on a network that drops incoming traffic instead of forwarding it normally. The intent of the RBL was that sites using it would refuse traffic from sites which supported spam — whether by actively sending spam, or in other ways. Before an address would be listed on the RBL, volunteers and MAPS staff would attempt repeatedly to contact the persons responsible for it and get its problems corrected. Such effort was considered very important before blackholing all network traffic, but it also meant that spammers and spam supporting ISPs could delay being put on the RBL for long periods while such discussions went on. Later, the RBL was also released in a DNSBL form and Paul Vixie encouraged the authors of sendmail and other mail software to implement RBL support in their clients. These allowed the mail software to query the RBL and reject mail from listed sites on a per-mail-server basis instead of blackholing all traffic. Soon after the advent of the RBL, others started developing their own lists with different policies. One of the first was Alan Brown's Open Relay Behavior-modification System (ORBS). This used automated testing to discover and list mail servers running as open mail relays—exploitable by spammers to carry their spam. ORBS was controversial at the time because many people felt running an open relay was acceptable, and that scanning the Internet for open mail servers could be abusive. In 2003, a number of DNSBLs came under denial-of-service attacks. Since no party has admitted to these attacks nor been discovered responsible, their purpose is a matter of speculation. However, many observers believe the attacks are perpetrated by spammers in order to interfere with the DNSBLs' operation or hound them into shutting down. In August 2003, the firm ''Osirusoft'', an operator of several DNSBLs including one based on the SPEWS data set, shut down its lists after suffering weeks of near-continuous attack. Technical specifications for DNSBLs came relatively late in RFC5782. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「DNSBL」の詳細全文を読む スポンサード リンク
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